Soil testing to determine phosphorus (P) availability to crops is a well established process. Today, however, there is increasing emphasis on relating existing or new soil tests to the potential for P loss from soils to surface waters. The objective of this study was to determine how well short-term soil P measurements (water soluble P (WSP), Mehlich-1 P, degree of P saturation (DPS), and 1-day desorbable P) predicted long-term P release and P sorption in relation to soil properties. Topsoils and subsoils with widely differing properties were collected from four sites in Northern Ireland, the Republic of Ireland, and the U.S. mid-Atlantic coastal plain, with topsoils and subsoils sampled at each site. All soils were analyzed for water soluble P, Mehlich-1 P, oxalate extractable Al, Fe, and P (Alox, Feox, Pox), degree of P saturation (DPS = (Pox/0.5[Alox+Feox]) × 100, free [Alox+Feox] = 0.5[Alox+Feox]−Pox), long-term desorbable P (using Fe-oxide-filled dialysis membranes), and long-term P sorption for "remaining P sorption capacity" (from a solution maintained at 5 mg P L−1). Long-term desorbable P followed a pattern of initial fast P release followed by a slower release of P that was still in progress after 39 days. Water soluble P, Mehlich-1 P, and the DPS were all correlated with the cumulative amount of P desorbed in 39 days (r = 0.82*, 0.79*, and 0.83*, respectively). However, for short-term (1 day) desorbable P, correlations followed the order WSP (r = 0.94***) > DPS (r = 0.83*) > Mehlich-1 P (r = 0.72*). When P was added to the soils, all of the soils exhibited an initial period of rapid P sorption, followed by a period of slower sorption still in progress after 38 days. The soil components found to be related most closely to remaining P sorption capacity were free [Alox+Feox] (r = 0.73*) and free Alox (r = 0.80*), indicating that amorphous Fe and Al are the major soil components responsible for long-term (38 days) P sorption. Overall, a single oxalate extraction for Al, Fe, and P proved to be most useful for predicting both long-term P release, through calculation of the DPS and for predicting the ability of the soils to sorb more P by calculating free [Alox+Feox].
Fertilizer phosphorus (P) can become immobilized in acidic soils through bonds with iron (Fe) and aluminum (Al). Two chelating agents, ethylenediamine tetraacetic acid disodium salt (EDTA) and hydroxyethyl ethylenediamine triacetic acid (HEEDTA), were tested in a greenhouse study for efficiency at increasing plant-available P to corn (Zea mays L.). Fertilizer P was added with or without chelate to the center of pots, simulating a starter band of P. Without the presence of chelates, biomass above and below ground increased linearly as P fertilizer rates increased at 0, 9.6, 19.3, 28.9, and 38.5 kg P ha−1. Applications of EDTA and HEEDTA did not significantly increase water-soluble P (WSP), Mehlich 1 P, and Mehlich 3 P compared to soils without chelates. Applications of EDTA increased P uptake in the belowground biomass. Despite previous research showing that chelates increased WSP in soils, a decrease in P sorption was not observed with the additions of chelating agents to soils.
Phytate is an organic form of P that is difficult to analyze in complex matrices. To test if high concentrations of aluminum (Al) and iron (Fe) hinder accurate quantification of phytate in dairy manure and broiler litter when measured by high-performance ion chromatography (HPIC), researchers spiked dairy manure and broiler litter samples with Al, Fe, and phytate. Samples were alkaline extracted, acidified, and filtered, and then phytate spike recovery was analyzed with HPIC. High concentrations of Fe did not hinder phytate recovery in manure or litter samples. While phytate recovery was complete at typical manure and litter Al concentrations, high concentrations of Al inhibited phytate recovery in litter samples and in some manure samples. Overall, alkaline extraction of dairy manure and broiler litter and analysis with HPIC proved to be relatively accurate, fast, and cheap within normal Al and Fe ranges, compared to the commonly used nuclear magnetic resonance (NMR) method.
The continuous assessment of grassland biomass during the growth season plays a vital role in making informed, location-specific management choices. The implementation of precision agriculture techniques can facilitate and enhance these decision-making processes. Nonetheless, precision agriculture depends on the availability of prompt and precise data pertaining to plant characteristics, necessitating both high spatial and temporal resolutions. Utilizing structural and spectral attributes extracted from low-cost sensors on unmanned aerial vehicles (UAVs) presents a promising non-invasive method to evaluate plant traits, including above-ground biomass and plant height. Therefore, the main objective was to develop an artificial neural network capable of estimating pasture biomass by using UAV RGB images and the canopy height models (CHM) during the growing season over three common types of paddocks: Rest, bale grazing, and sacrifice. Subsequently, this study first explored the variation of structural and color-related features derived from statistics of CHM and RGB image values under different levels of plant growth. Then, an ANN model was trained for accurate biomass volume estimation based on a rigorous assessment employing statistical criteria and ground observations. The model demonstrated a high level of precision, yielding a coefficient of determination (R2) of 0.94 and a root mean square error (RMSE) of 62 (g/m2). The evaluation underscores the critical role of ultra-high-resolution photogrammetric CHMs and red, green, and blue (RGB) values in capturing meaningful variations and enhancing the model’s accuracy across diverse paddock types, including bale grazing, rest, and sacrifice paddocks. Furthermore, the model’s sensitivity to areas with minimal or virtually absent biomass during the plant growth period is visually demonstrated in the generated maps. Notably, it effectively discerned low-biomass regions in bale grazing paddocks and areas with reduced biomass impact in sacrifice paddocks compared to other types. These findings highlight the model’s versatility in estimating biomass across a range of scenarios, making it well suited for deployment across various paddock types and environmental conditions.
Surface broadcast of dairy slurry is a common practice; however, concerns over nuisance odors and nutrient losses have prompted research into alternatives. Manure injection is one practice that addresses these concerns but is not widely adopted. Therefore, two studies were conducted to quantify NH3-N loss by volatilization, impacts on soil N cycling, and microbial response between surface broadcast and subsurface injection of dairy slurry. A constant air flow volatilization chamber system measured NH3-N losses and soil inorganic N, mineralizable carbon, and active microbial biomass. A 40-day static air incubation was performed to study nitrogen transformations over a longer period after application. Statistical significance was evaluated at the α = 0.05 level. In the volatilization study, subsurface injection reduced NH3-N losses by 98% and 87% in a clay loam and sandy loam, respectively, resulting in greater soil inorganic nitrogen compared with surface application. There were no significant differences in active microbial biomass between treatments. Surface application prompted greater microbial respiration in the sandy loam, but there were no significant differences between treatments in the clay loam. In the static incubation study, differences in soil NO3−-N became significant on day 28, and by day 40, injection showed increases in soil NO3−-N of 13% and 26% in the sandy loam and clay loam, respectively, relative to surface application. While the effect of subsurface injection on soil microbial response was unclear, it remains a tool that can greatly reduce NH3-N losses by volatilization and increase soil plant available nitrogen.
Summary The test for the degree of phosphorus (P) saturation (DPS) of soils is used in northwest Europe to estimate the potential of P loss from soil to water. It expresses the historic sorption of P by soil as a percentage of the soil's P sorption capacity (PSC), which is taken to be α (Al ox + Fe ox ), where Al ox and Fe ox are the amounts of aluminium and iron extracted by a single extraction of oxalate. All quantities are measured as mmol kg soil −1 , and a value of 0.5 is commonly used for the scaling factor α in this equation. Historic or previously sorbed P is taken to be the quantity of P extracted by oxalate (P ox ) so that DPS = P ox /PSC. The relation between PSC and Al ox , Fe ox and P ox was determined for 37 soil samples from Northern Ireland with relatively large clay and organic matter contents. Sorption of P, measured over 252 days, was strongly correlated with the amounts of Al ox and Fe ox extracted, but there was also a negative correlation with P ox . When PSC was calculated as the sum of the measured sorption after 252 days and P ox , the multiple regression of PSC on Al ox and Fe ox gave the equation PSC = 36.6 + 0.61 Al ox + 0.31 Fe ox with a coefficient of determination ( R 2 ) of 0.92. The regression intercept of 36.6 was significantly greater than zero. The 95% confidence limits for the regression coefficients of Al ox and Fe ox did not overlap, indicating a significantly larger regression coefficient of P sorption on Al ox than on Fe ox . When loss on ignition was employed as an additional variable in the multiple regression of PSC on Al ox and Fe ox , it was positively correlated with PSC. Although the regression coefficient for loss on ignition was statistically significant ( P < 0.001), the impact of this variable was small as its inclusion in the multiple regression increased R 2 by only 0.028. Values of P sorption measured over 252 days were on average 2.75 (range 2.0–3.8) times greater than an overnight index of P sorption. Measures of DPS were less well correlated with water‐soluble P than either the Olsen or Morgan tests for P in soil.
Poultry litter is a common organic amendment in agricultural production, but nutrient losses can reduce its effectiveness as a fertilizer. Three experiments were conducted to evaluate ammonia nitrogen (NH3-N) volatilization, N availability, and runoff losses of nutrients by conducting a closed chamber volatilization study, a soil incubation, and a rainfall simulation. In all studies, poultry litter was applied at a rate of 6.7 Mg · ha−1 either on the surface or injected and compared with an unamended control. In the volatilization and soil incubation studies, Braddock Loam and Bojac Sandy Loam surface soils were compared. Of the ammonium N added, cumulative loss of NH3-N by volatilization was 3% from injected and 121% from surface applied poultry litter after 7 days in the Loam. In the Sandy Loam, cumulative loss of NH3-N was 9% from injected and 153% from surface applied poultry litter after 7 days. After a 40-day soil incubation, injection increased total inorganic N by 52% and 99% for the Loam and Sandy Loam soils, respectively, when compared with surface application. Injection reduced total Kjeldahl N by 59%, total Kjeldahl P by 53%, dissolved reactive P, dissolved nitrate N by 73%, and dissolved NH3-N in runoff by 99%, compared with surface application. Injection reduced NH3-N volatilization and nutrients in runoff to levels of the control. These studies show that injection increases plant available N while decreasing losses through volatilization and runoff.
Biochar created from poultry litter is a way to produce a value-added soil amendment that is lighter and less expensive to transport out of manure nutrient excess areas, but effects on soil properties are unknown. Two studies were conducted with a Sandy loam and a Silt loam. First, lettuce seeds were germinated across biochar incorporation rates from 0% to 100% biochar, and second, a greenhouse trial was conducted in which peppers were grown in soils with up to 5% biochar by weight. Elemental analysis was completed on the biochar, and soils were analyzed for bulk density, water-holding capacity, pH, cation exchange capacity, and extractable nutrients. Biochar increased lettuce germination by almost 50% in the Sandy loam at low rates but became toxic at rates greater than 2.5% in both soils probably due to salt toxicity. Water-holding capacity increased linearly with biochar additions. For example, adding 15% biochar nearly doubled the water-holding capacity of the Sandy loam from 15% to 27%. The biochar had a pH of 9.3, and additions increased the pH of both soils. Total phosphorus (P) in the biochar was 43 g kg−1, and although almost none of this was water soluble in the pure biochar, the Mehlich 1 P and Olsen P were greatly increased in biochar amended soils. Biochar consistently increased the cation exchange capacity only at high rates. Biochar made from poultry litter showed several benefits as a soil amendment, but application rates would be limited by soil test P and pH.
